SAN FRANCISCO — If recreational marijuana becomes a big over-the-counter business in California, it likely won’t be because of big donations to a ballot measure to legalize the drug.

No one’s pouring much money into either side of the high-profile battle to legalize possession and cultivation of limited amounts of pot for adults — not even the thriving medical marijuana industry, a seemingly natural base of support for a measure being sold as a way to raise tax revenue for the cash-strapped state.

Supporters of the measure had raised $2.1 million as of Tuesday, the latest deadline for campaigns to report their contributions. Opponents had raised just more than $210,000, much of it from law enforcement sources.

Both sides had about the same small amount of cash on hand: about $54,000 for opponents and $67,000 for the supporters.

Roger Salazar, a spokesman for the opponents, blames the tepid fundraising in part on higher profile contests — such as the race for governor — drawing attention and money. He also said some voters inclined to oppose the measure might not give money because they have a hard time imagining the status quo could change.

“People tend to look at it and say, ‘Of course it’s going to lose, who’s going to vote for that?’” Salazar said.

Also, ballot measure watchers said initiatives that deal with social issues typically attract less funding than measures that involve major industries such as oil, energy and insurance.

“There’s just no economic interest there,” said John Matsusaka, president of the Initiative and Referendum Institute at the University of Southern California.

The one glaring exception is Proposition 8, the 2008 measure that banned same-sex marriage in the state. Groups for and against the measure spent more than $83 million, a national record for a ballot measure on a social issue.

In the pot debate, both sides have relied on media attention rather than brimming campaign chests to get their messages out. The approach seems to be working.

In a recent Field Poll, 84 percent of respondents said they had heard of Proposition 19, compared with under 40 percent for other major measures on the ballot Nov. 2.

“People have strong feelings about this. They’re not easily swayed. TV advertising doesn’t have as big an effect, pro or con,” said the measure’s main backer, Richard Lee, a one-time rock concert lighting technician turned medical marijuana entrepreneur. Nearly three-quarters of the money raised by supporters came from Lee’s businesses.

Recent polling does suggest that many likely voters have made up their minds: Fewer than 10 percent of likely voters said they were undecided on the proposition, according to the most recent Field and Public Policy Institute of California polls. The measure was ahead in both polls.

Still, supporters are faced with the irony of having little funding for a measure billed as a moneymaker for California.

The measure has sharply divided the medical marijuana industry, which could lose out if cities allow other retailers to sell the drug. Users would no longer need recommendations from doctors who specialize in medical marijuana to obtain the drug, and illicit growers could see legalized marijuana drive prices into a tailspin.

Lanette Davies, who runs the CannaCare medical marijuana dispensary in Sacramento, said she believes that the ballot measure’s provision allowing local governments to regulate the sale of marijuana will lead cities and counties to curb access to marijuana for both recreational and medical use.

“It just undermines what we’ve done so far,” she said.

Opponents of the measure are being heavily outfunded, as they were on some past pro-drug measures.

But ballot measure backers must typically spend a lot to convince voters to support change, while opponents can sometimes succeed simply by sowing reasonable doubt, Matsusaka said.

“You can vastly outspend your opponent on the pro side and still lose,” he said.